Electron emitting cathode and method of forming same



Oct. 6, 1931. F. s. M CULLOUGH 1,826,011

ELECTRON EMITTING CATHODE AND METHOD OF FORMING SAME Filed Sep 1923 Patented Oct. 6, 1931 ATENT OFFICE FREDERICK S. MCGULLOUGH, OF WILKINSBURG, PENNSYLVANIA ELECTRON EMITTING CATHODE AND METHOD OF FORMING SAME Application filed September 17, 1923. Serial No. 663,143.

This invention relates to a cathode structure for use in connection with space discharge devices, as for instance, thermionic tubes, and to the method of forming such structures.

The invention has for one of its primary objects to provide a coated core to be used as a cathode wherein the coating is applied directly to the surface of the core without the introduction of foreign substances, as has heretofore been done to bind or cement the coating on the core, the mixing or introduction of any foreign substance being entirely eliminated. This decreases the voltage drop between the core and the coating to the greatest possible minimum.

A further important object of the invention is the method for applying a coating to a core in such manner that the coating will be more securely retained on the core and less subject to disintegration and cracking off under varying temperatures and electrostatic conditions.

Briefly, the invention consists in raising the temperature of the core to a high degree, and at the same time maintaining it in a mist or atmosphere of the coating solution or substance. V

The nature of the invention may be more readily understood by reference to the ac-. companying drawing, in which the figure represents a somewhat diagrammatic view of an apparatus for carrying out the invention, the figure representing a vertical sectional view of a coating appartus.

In the drawing, 5 designates a quartz tube, around which is a coil 6. The tube and coil are enclosed in a heat insulating envelope 7. When the coil 6 is connected in an alternating current circuit, preferably a circuit alternating at radio frequency. this device forms an electric furnace of the induction type when a metal object to be heated is introduced into the chamber 8 within the tube. Instead of being of the induction type, the coil could be a resistance for heating by radiation, or induction and radiation may both be used.

Attached to the lower end of tube 5 is another tube or vessel 8a having a pipe 9 opening into its lower end.

At 10 and 11 are wheels, wheel 10 preferably being located above the tube 5 and wheel 11 preferably being below the lower end of this tube. Vheel 10 may be driven from a pulley wheel 12 through belt 13, a handle 14 or other suitable operating means being provided for wheel 12. Passing over wheels 10 and 11 is a wire or ribbon which provides the metal core for the cathode structure to be formed. In carrying out the process, the vessel 8a 1s partially filled with a mixture and solution of the oxide or other substance to be coated on the core. A blast of gas is forced into this solution through pipe 9, filling the upper part of vessel 8a and chamber 8 with a mist. The temperature of the core is then raised electrically to a high degree. Under these conditions, the mist of coating material Wlll form a closely adhering coating on the core. The core may be formed of platinum or iridium in which case a blast of air may be passed through pipe 9. A metal as nickel may also be used for the core in which case it is preferable to use some reducing gas as hydrogen or carbon dioxide.

By manipulation of wheel 12, the wire ma be continuously treated until its entire length has been covered.

The coating is one designed, of course, to give hlgh electron emissivity, certain oxides being preferable, such for instance, as oxides of barium and strontium, or of thorium. While I am aware that it has heretofore been the practice to use oxide or other coatings, it has been the practice to introduce foreign substances also, so that the oxide is not pure and free of foreign substances. The solution used may be a solution of the oxide in water or other solvent which will evaporate without changing the character of the substanceto be deposited.

I claim as my invention:

1. The method of forming a cathode struc- 5 Y ture to increase the normal electron emissionof its core which consists in raising the temperature of the metal core while subjecting the core to a mist of coating material produced by passing a gas through a solution of 0 said coating material which said material is at a temperature below its boiling point.

2. The method of forming a continuous cathode structure to increase the normal electron emission of its core which consists in raising the temperature of the metal core by passing it down through a heated area, thence passing it through a mist of coating material produced by passing a gas through a liquid solution containing said coating material and passing the core back through the heated area after being coated.

3. The method of forming a coated. cathode structure which consists in forming a solution containing a coating material and an inert solvent, generating a mist from this solution and passing a continuous core through a heated area, thence through the mist of said solution and back through the furnace whereby the coating is securely formed on the core.

4. The method of forming a coated cathode structure which consists in forming a solution containing a coating material of high electron emissivity in an inert solvent and placing the same in a receptacle, generating a mist from this solution by passing a gas through the bottom of said receptacle and up through said solution and passing a metal core while heated through the said mist and drying the same whereby a coating is deposited and formed on said core.

In testimony whereof I hereunto afix my signature.

FREDERICK S. MGCULLOUGH, 

